Dual stage air bag inflator

ABSTRACT

An apparatus ( 12 ) provides inflation fluid for inflating an inflatable vehicle occupant protection device ( 14 ). The apparatus ( 12 ) includes a primary housing ( 20 ), a primary inflation fluid source ( 100 ), a secondary housing ( 70 ), and a secondary inflation fluid source ( 200 ). The primary housing ( 20 ) is constructed from sheet metal by stamping. The primary inflation fluid source ( 100 ) is located in the primary housing ( 20 ). The primary inflation fluid source ( 100 ) is actuatable to effect a primary flow of inflation fluid out of the primary housing ( 20 ) to inflate the inflatable device ( 14 ). The secondary housing ( 70 ) is constructed from sheet metal by stamping. The secondary housing ( 70 ) is disposed within the primary housing ( 20 ). The secondary inflation fluid source ( 200 ) is located in the secondary housing. The secondary inflation fluid source ( 200 ) is actuatable to affect a secondary flow of inflation fluid to supplement the primary flow of inflation fluid. The secondary housing ( 70 ) has a first portion ( 77 ) that moves at least partially out of engagement with a second portion ( 74 ) of the secondary housing ( 70 ) when the secondary inflation fluid source is actuated.

RELATED APPLICATION

This application is a divisional of U.S. Ser. No. 13/895,406, filed May16, 2013, which is a divisional of U.S. Ser. No. 11/634,504, filed Dec.6, 2006, which issued as U.S. Pat. No. 8,444,179 on May 21, 2013.

TECHNICAL FIELD

The present invention relates to an apparatus for inflating aninflatable vehicle occupant protection device and, more particularly, toan inflator for the inflatable vehicle occupant protection device.

BACKGROUND OF THE INVENTION

An inflatable vehicle occupant protection device, such as an air bag, isdeployed upon the occurrence of a vehicle collision. The air bag is partof a conventional vehicle occupant protection apparatus that includes acollision sensor and an inflator. The inflator includes a housing and aninflation fluid source in the housing. Upon sensing the occurrence of anevent for which inflation of the air bag is desired, the inflator isactuated and produces inflation fluid under pressure in the inflatorhousing. The pressurized inflation fluid is directed out of the inflatorhousing and inflates the air bag into the vehicle occupant compartmentto help protect the vehicle occupants.

When the inflator is actuated at an elevated ambient temperature, thepressure of the inflation fluid in the inflator housing increases. Aninflator must be strong enough structurally to contain these elevatedpressures. If the pressure in the inflator housing is increased in thismanner, the mass flow rate of the inflation fluid flowing into the airbag may also increase.

SUMMARY OF THE INVENTION

The present invention relates to an apparatus for providing inflationfluid for inflating an inflatable vehicle occupant protection device.The apparatus includes a primary housing, a primary inflation fluidsource, a secondary housing, and a secondary inflation fluid source. Theprimary housing is constructed from sheet metal by stamping. The primaryinflation fluid source is located in the primary housing. The primaryinflation fluid source is actuatable to affect a primary flow ofinflation fluid out of the primary housing to inflate the inflatabledevice. The secondary housing is constructed from sheet metal bystamping. The secondary housing is disposed within the primary housing.The secondary inflation fluid source is located in the secondaryhousing. The secondary inflation fluid source is actuatable to affect asecondary flow of inflation fluid to supplement the primary flow ofinflation fluid. The secondary housing has a first portion that moves atleast partially out of engagement with a second portion of the secondaryhousing when the secondary inflation fluid source is actuated.

The present invention relates to an inflator for providing inflationfluid for inflating an inflatable vehicle occupant protection device.The inflator includes a primary housing, a primary inflation fluidsource, a secondary housing, and a secondary inflation fluid source. Theprimary housing has an upper wall and a lower wall opposite the upperwall. The primary housing is constructed from sheet metal by stamping.The primary inflation fluid source is disposed within the primaryhousing and is actuatable to deform the primary housing to move theupper wall and the lower wall away from each other. The secondaryhousing is constructed from sheet metal by stamping. The secondaryhousing is disposed within the primary housing. The secondary housinghas an upper portion abutting the upper wall of the primary housing anda lower portion abutting the lower wall of the primary housing. Thesecondary inflation fluid source is disposed within the secondaryhousing and is actuatable to move the upper portion of the secondaryhousing at least partially out of engagement with the tower portion ofthe secondary housing subsequent to the primary housing being deformedby the primary inflation fluid source.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the present invention will become apparent to thoseskilled in the art to which the present invention relates from readingthe following description with reference to the accompanying drawings,in which:

FIG. 1 is a schematic view of a vehicle occupant protection apparatusincluding an inflator constructed in accordance with the presentinvention;

FIG. 2 is a sectional view of an inflator in an unactuated condition inaccordance with a first embodiment of the present invention;

FIG. 3 is a schematic view of the inflator of FIG. 2 in an actuatedcondition;

FIG. 4 is a schematic view of the inflator of FIG. 2 in another actuatedcondition;

FIG. 5 is a sectional view of an inflator in an unactuated condition inaccordance with a second embodiment of the present invention;

FIG. 6 is a schematic view of the inflator of FIG. 5 in an actuatedcondition;

FIG. 7 is a schematic view of the inflator of FIG. 5 in another actuatedcondition; and

FIG. 8 is a sectional view along line 8-8 in FIGS. 2 and 5.

DESCRIPTION OF EMBODIMENTS

The present invention relates to an apparatus for providing inflationfluid for inflating an inflatable vehicle occupant protection device. Asrepresentative of the present invention, FIG. 1 illustratesschematically an inflator 10 that forms part of a vehicle occupantprotection apparatus 12.

The apparatus 12 includes an inflatable vehicle occupant protectiondevice 14. The protection device 14, for example, may be a frontaldriver or passenger air bag for helping to protect a vehicle occupant.Other inflatable vehicle occupant protection devices that can be used inaccordance with the present invention include, for example, but are notlimited to inflatable seat belts, inflatable knee bolsters, inflatablehead liners, inflatable side curtains, and knee bolsters operated byinflatable air bags.

The inflator 10 is actuatable to provide inflation fluid for inflatingthe air bag 14. When the air bag 14 is inflated, it extends into avehicle occupant compartment (not shown) to help protect a vehicleoccupant.

The apparatus 12 also includes a sensor 16 for sensing the occurrence ofan event for which inflation of the air bag 14 is desired. The sensor 16is operatively connected to a controller 18. The controller 18 isoperative to actuate the inflator 10 in response to conditions sensedvia the sensor 16. For example, the sensor 16 may be operative to sensevehicle acceleration or deceleration and provide a signal indicative ofthe sensed acceleration.

As shown in FIG. 2, a first embodiment of the inflator 10 includes agenerally cylindrical housing 20. Referring to FIGS. 2 and 8, theinflator 10 has a generally cylindrical configuration. The housing 20(FIG. 2) includes a first or upper housing pad 30, referred to herein asa diffuser, and a second or lower housing part 40, referred to herein asa closure.

The diffuser 30 has a downwardly open, cup-shaped configuration centeredon a first primary axis 51 of the inflator 10. The diffuser 30 includesa radially extending upper wall 42 and an axially extending side wall44. As shown in FIG. 2, the upper wall 42 of the diffuser 30 may have agenerally planar configuration (FIG. 2). The upper well 42 could have analternative configuration (not shown), such as a domed or concaveconfiguration projecting away from the closure 40.

The side wall 44 of the diffuser 30 has a cylindrical configurationcentered on the first axis 51. A plurality of inflation fluid outlets,or exhaust ports, 56 are disposed in a circular array about thecylindrical side wall 44. Each one of the inflation fluid outlets 56extends radially through the side wall 44. The outlets 56 enable flow ofinflation fluid out of the inflator 10 to inflate the air bag 14. Theoutlets 56, as a group, have a fixed, predetermined flow area.

The closure 40 has a shallow dished configuration including a radiallyextending lower wall 62. The lower wall 62 of the closure 40 has agenerally domed configuration and projects away from the diffuser 30.The lower wall 62 has an inner surface 66 presented toward an innersurface 46 of the upper wall 42 of the diffuser 30. A circular opening68 in the lower wall 62 is centered on a second axis 52 that is parallelto and radially offset from the first axis 51.

The closure 40 is centered on the first axis 51. An annular inflatormounting flange 64 extends radially outward from the side wall 44 of thediffuser 30 at a location below (as viewed in FIG. 2) the inflationfluid outlets 56 of the diffuser 30.

The closure 40 is welded to the lower terminal end 47 of the diffuser 30with a single, continuous circular weld 69. The diffuser 30 and closure40 together define a primary combustion chamber 99.

The inflator 10 further includes a primary igniter assembly 100 and asecondary igniter assembly 200. The primary igniter assembly 100 ismounted to a primary mounting portion 48 of the closure 40. The primarymounting portion 48 is formed in the closure 40 by stamping. The primarymounting portion 48 is centered en a third axis 53 parallel to endradially offset from the first and second axes 51, 52. The primarymounting portion 48 extends axially toward the upper wall 42 of thediffuser 30. The primary mounting portion 48 has a recessed andgenerally cup-shaped configuration with a generally cylindrical sidewall 49, an end wall 50, and an opening 54 that extends through the endwall.

The primary igniter assembly 100 may be a known device that iselectrically actuatable to generate combustion products. The primarymounting portion 48 helps position the primary igniter assembly 100 onthe closure 40. The primary igniter assembly 100 is press fit into theopening 54 in the end wall 50 of the primary mounting portion 48 tosecure and position the primary igniter assembly in the primarycombustion chamber 99. The primary igniter assembly 100 is thus disposedat a location in the inflator 10 centered on the third axis 53.

The inflator 10 further includes a secondary igniter cup 70 for helpingto secure the secondary igniter assembly 200 in the inflator. Thesecondary igniter cup 70 is centered on the second axis 52. Thesecondary igniter cup 70 includes a radially extending lower wall 72 andan axially extending cylindrical side wall 74. The lower wall 72 of thesecondary igniter cup 70 has a domed or concave configuration projectingtoward the closure 40 and a central secondary mounting portion 76centered on the second axis 52 and projecting away from the closure. Thelower wall 72 could have an alternative configuration (not shown), suchas a planar configuration.

The secondary mounting portion 75 is stamped in the lower wall 72 of theof the secondary igniter cup 70. The secondary mounting portion 75 has arecessed and generally cup-shaped configuration with an axiallyextending side wall 82, an end wall 83, and an opening 84 that extendsthrough the end wall. The secondary igniter assembly 200 is press fitinto the opening 84 of the secondary mounting portion 75 to secure thesecondary igniter assembly in position in a secondary combustion chamber79. The secondary igniter assembly 200 is thus supported in the inflator10 at a position centered on the second axis 52 and offset from thefirst axis 51 and the third axis 53.

A secondary cap 77 is secured to the upper open end of the side wall 74to define the secondary combustion chamber 79. The secondary cap 77 issecured to the secondary igniter cup 70 by an interference fit. Thesecondary cap 77 has a domed configuration projecting away from theclosure 40. The secondary end cap 77 could have an alternativeconfiguration (not shown), such as a planar configuration. The secondarycap 77 has an inner surface 73 presented toward an inner surface 76 ofthe lower wall 72.

Prior to welding the diffuser 30 to the closure 40, the secondaryigniter assembly 200, secondary cup 70, and secondary cap 77 areassembled and placed within the primary combustion chamber 99 of thediffuser 30 such that the secondary cap 77 abuts the inner surface 46 ofthe diffuser. The closure 40 is then positioned so that the circularopening 68 is aligned with the lower end of the secondary igniterassembly 200 (FIG. 2). An annular elastomeric seal 81 may be disposedbetween the lower wall 72 of the secondary igniter cup 70 and the innersurface 66 of the closure 40.

The inflator 10 further includes a first actuatable inflation fluidsource 110 in the form of a primary solid propellant. The primarypropellant 110 is disposed in the primary combustion chamber 99, atleast partially encircling or surrounding the side wall 74 of thesecondary igniter cup 70. The primary propellant 110 is a known materialthat is ignitable via actuation of the primary igniter assembly 100. Theprimary propellant 110, when ignited, produces inflation fluid in theform of gas under pressure for inflating the air bag 14. The primarypropellant 110 is illustrated as being provided in the form of generallycylindrical pellets filling or substantially filling the primarypropellant chamber 99. Alternatively, the primary propellant 110 couldbe provided in the form of small discs or tablets.

The inflator 10 includes a second actuatable inflation fluid source 210in the form of a secondary solid propellant disposed in the secondarycombustion chamber 79. The secondary propellant 210 is a known materialthat is ignitable via actuation of the secondary igniter assembly 200.The secondary propellant 210, when ignited, produces inflation fluid inthe form of gas under pressure for inflating the air bag 14. Thesecondary propellant 210 may be made from the same material as theprimary propellant 110. The secondary propellant 210 is illustrated asbeing provided in the form of a plurality of small generally cylindricalpellets filling or substantially filling the secondary propellantchamber 79. Alternatively, the secondary propellant 210 could beprovided in the form of discs or tablets.

Upon sensing the occurrence of an event for which inflation of the airbag 14 is desired, the sensor 16 provides a signal to the controller 18.The controller 18 is operative to actuate selectively either the primaryigniter assembly 100 alone or both the primary igniter assembly and thesecondary igniter assembly 200 in response to the signal from thesensor. If the signal is above a first predetermined threshold level,but below a second predetermined threshold level, the controller 18actuates only the primary igniter assembly 100. The primary igniterassembly 100, when actuated, ignites the primary propellant 110 in theprimary combustion chamber 99. The primary propellant 110 combusts andproduces inflation fluid under pressure in the primary propellantchamber 99. The pressure in the primary propellant chamber 99 risesrapidly.

The assembled secondary igniter cup 70 and secondary cap 77 during thistime block flow of combustion products from the primary propellantchamber 99 into the secondary propellant chamber 79 (FIG. 3). Thisprevents ignition of the secondary propellant 210 when the controller 18actuates only the primary igniter assembly 100.

The material thickness of the diffuser 30 and closure 40 is selected sothat the upper and lower walls 42 and 62 deform in response to inflationfluid pressure in the primary combustion chamber 99. Specifically, theupper wall 42 of the diffuser 30 deforms axially outward (in an upwarddirection as viewed in FIG. 3). Simultaneously, the lower wall 62 of theclosure 40 deforms axially outward in an opposite downward direction asviewed in FIG. 3. The degree to which the walls 42 and 62 deform ordeflect is dependent upon the pressure in the primary combustion chamber99. As the fluid pressure in the primary combustion chamber 99increases, the degree to which the walls 42 and 62 deflect alsoincreases.

As the walls 42 and 82 of the diffuser 30 and closure 40, respectively,move away from each other, the pressure of the inflation fluid in theprimary propellant chamber 99 forces the primary igniter assembly 100against the primary mounting portion 48 of the closure 40. The forceexerted by the inflation fluid on the primary igniter assembly 100affects a fluid-tight seal between the primary igniter assembly 100 andthe closure 40.

As a result of the deformation of the walls 42 and 62 of the diffuser 30and closure 40, the distance between the upper wall 42 of the diffuserand the lower wall 62 of the closure increases. Therefore, the secondaryigniter cup 70 is no longer trapped axially between the diffuser 30 andthe closure 40. The pressure of the inflation fluid in the primarypropellant chamber 99, acting in a downward direction (as viewed in FIG.3) on the secondary cap 77 holds the secondary cap in engagement withthe side wall 74 of the secondary igniter cup 70.

The inflation fluid flows out of the primary propellant chamber 99,through an annular filter 91, and toward the inflation fluid outlets 56.The fluid outlets 56 direct the inflation fluid to flow out of thediffuser 30 to the air bag 14.

If the signal provided by the sensor 16 is above a second predeterminedthreshold level, greater than the first threshold level, the controller18 actuates both the primary igniter assembly 100 and the secondaryigniter assembly 200. The actuation of the primary igniter assembly 100results in ignition of the primary propellant 110, as described above.Inflation fluid produced by the primary propellant 110 deforms thediffuser 30 and closure 40, and flows out of the inflator 10, asdescribed above.

The secondary igniter assembly 200, when actuated, ignites the secondarypropellant 210. The secondary propellant 210 produces combustionproducts that increase the pressure in the secondary combustion chamber79. This increased pressure acts on the secondary cap 77 and causes thesecondary cap to move out of engagement with the side well 74 of thesecondary igniter cup 70 (FIG. 4). This movement of the secondary cap 77is allowed due to the clearance created by the deformation of thediffuser 30 and the closure 40.

The combustion products of the secondary propellant 210 are therebycombined with the combustion products of the primary propellant 110 inthe primary combustion chamber 99. The resulting increase of pressure inthe primary combustion chamber 99 causes the diffuser 30 and closure 40to deform more than when only the primary propellant 110 is ignited(FIG. 4). The combined combustion products of the secondary propellant210 and the primary propellant 110 flow through the filter 91 and out ofthe inflator 10 in the manner described above.

The diffuser 30, the closure 40, the secondary igniter cup 70, and thesecondary cap 77 are fabricated from sheet metal by a stamping process.The relative absence of machined or other precise tolerance featureswithin the inflator 10 reduces production and assembly costs while stillmaintaining the functional relationships between the internal pads ofthe inflator 10.

As shown in FIG. 5, a second embodiment of the inflator 10 a includes agenerally cylindrical housing 20 a. Referring to FIGS. 5 and 8, theinflator 10 a has a generally cylindrical configuration. The housing 20a (FIG. 5) includes a first or upper housing part 30 a, referred toherein as a diffuser, and a second or lower housing part 40 a, referredto herein as a closure.

The diffuser 30 a has a downwardly open, cup-shaped configurationcentered on a first primary axis 51 a of the inflator 10 a. The diffuser30 a includes a radially extending upper wall 42 a and an axiallyextending side wall 44 a. As shown in FIG. 5, the upper wall 42 a of thediffuser 30 a may have a generally domed or concave configurationprojecting generally away from the closure 40. The upper wall 42 a couldalternatively have a generally planar configuration (not shown).

The side wall 44 a of the diffuser 30 a has a cylindrical configurationcentered on the first axis 51 a. A plurality of inflation fluid outlets,or exhaust ports, 56 a are disposed in a circular array about thecylindrical side wall 44 a. Each one of the inflation fluid outlets 56 aextends radially through the side wall 44 a. The outlets 56 a enableflow of inflation fluid out of the inflator 10 a to inflate the air bag14. The outlets 56 a, as a group, have a fixed, predetermined flow area.

The closure 40 a has a cup-shaped configuration including a radiallyextending lower wall 62 a. The lower wall 62 a of the closure 40 a has agenerally domed configuration and projects away from the diffuser 30 a.The lower wall 62 a has an inner surface 66 a presented toward an innersurface 46 a of the upper wall 42 a of the diffuser 30 a. A firstcircular opening 68 a in the lower wall 62 a is centered on a secondaxis 52 a that is parallel to and radially offset from the first axis 51a. A second circular opening 69 a in the lower wall 62 a is centered ona third axis 53 a that is parallel to and radially offset from the firstaxis 51 a and the second axis 52 a.

The closure 40 a is centered on the first axis 51 a. The closure 40 a iswelded to a lower terminal end 47 a of the diffuser 30 a with a single,continuous circular weld 89 a. The diffuser 30 a and closure 40 atogether define a primary combustion chamber 99 a.

The inflator 10 a further includes a primary igniter assembly 100 a anda secondary igniter assembly 200 a. The primary igniter assembly 100 ais mounted to a primary mounting portion 48 a of the closure 40 a. Theprimary mounting portion 48 a is centered on the third axis 53 a. Theprimary mounting portion 48 a extends axially toward the upper wall 42 aof the diffuser 30 a. The primary mounting portion 48 a has a generallyplanar configuration and includes the second circular opening 69 a thatextends through the primary mounting portion.

The primary igniter assembly 100 a may be a known device that iselectrically actuatable to generate combustion products. The primarymounting portion 48 a helps position the primary igniter assembly 100 aon the closure 40 a. The primary igniter assembly 100 a is disposed inthe second circular opening 69 a and welded to the primary mountingportion 48 a to secure and position the primary igniter assembly in theprimary combustion chamber 99 a. The primary igniter assembly 100 a isthus disposed at a location in the inflator 10 a centered on the thirdaxis 53 a.

The inflator 10 a further includes a secondary igniter cup 70 a forhelping to secure the secondary igniter assembly 200 a in the inflator.The secondary igniter cup 70 a is centered on the second axis 52 a. Thesecondary igniter cup 70 a includes a radially extending lower wall 72 aand an axially extending cylindrical side wall 74 a. The lower wall 72 aof the secondary igniter cup 70 a has a generally dome-shapedconfiguration with a central mounting portion 75 a centered on thesecond axis 52 a and projecting toward the closure 40 a. The lower wall72 a could have an alternative configuration (not shown), such as aplanar configuration.

The central mounting portion 75 a has an opening 78 a that extendsthrough the central mounting portion. The secondary igniter assembly 200a is disposed in the opening 78 a of the central mounting portion 75 aand welded to the central mounting portion for positioning the secondaryigniter assembly in a secondary combustion chamber 79 a. The secondaryigniter assembly 200 a is thus supported in the inflator 10 a at aposition centered on the second axis 52 a and offset from the first axis51 a and the third axis 53 a.

A secondary cap 77 a is secured to the upper open end of the side wall74 a to define the secondary combustion chamber 79 a. The secondary cap77 a is secured to the secondary igniter cup 70 a by an interferencefit. The secondary cap 77 a has a domed configuration projecting awayfrom the closure 40 a. The secondary cap 77 a could have an alternativeconfiguration (not shown), such as a planar configuration. The secondarycap 77 a has an inner surface 73 a presented toward an inner surface 76a of the lower wall 72.

Prior to welding the diffuser 30 a to the closure 40 a, the secondaryigniter assembly 200 a, secondary igniter cup 70 a, and secondary cap 77a are assembled and placed within the primary combustion chamber 99 a ofthe diffuser 30 a such that the secondary cap 77 a abuts the innersurface 46 a of the diffuser. The closure 40 a is then positioned sothat the circular opening 68 a is aligned with the lower end of thesecondary igniter assembly 200 a (FIG. 5). An annular elastomeric seal81 a may be disposed between the lower wall 72 a of the secondaryigniter cup 70 a and the inner surface 66 a of the closure 40 a.

The inflator 10 a further includes a first actuatable inflation fluidsource 110 a in the form of a primary solid propellant. The primarypropellant 110 a is disposed in the primary combustion chamber 99 a, atleast partially encircling or surrounding the side wall 74 a of thesecondary igniter cup 70 a. The primary propellant 110 a is a knownmaterial that is ignitable via actuation of the primary igniter assembly100 a. The primary propellant 110 a, when ignited, produces inflationfluid in the form of gas under pressure for inflating the air bag 14.The primary propellant 110 a is illustrated as being provided in theform of generally cylindrical pellets filling or substantially fillingthe primary propellant chamber 99 a. Alternatively, the primarypropellant 110 a could be provided in the form of smell discs ortablets.

The inflator 10 a includes a second actuatable inflation fluid source210 a in the form of a secondary solid propellant disposed in thesecondary combustion chamber 79 a. The secondary propellant 210 a is aknown material that is ignitable via actuation of the secondary igniterassembly 200 a. The secondary propellant 210 a, when ignited, producesinflation fluid in the form of gas under pressure for inflating the airbag 14. The secondary propellant 210 a may be made from the samematerial as the primary propellant 110 a. The secondary propellant 210 ais illustrated as being provided in the form of a plurality of smallgenerally cylindrical pellets filling or substantially filling thesecondary propellant chamber 79 a. Alternatively, the secondarypropellant 210 a could be provided in the form of discs or tablets.

Upon sensing the occurrence of an event for which inflation of the airbag 14 is desired, the sensor 16 provides a signal to the controller 18.The controller 18 is operative to actuate selectively either the primaryigniter assembly 100 a alone or both the primary igniter assembly andthe secondary igniter assembly 200 a in response to the signal from thesensor. If the signal is above a first predetermined threshold level butbelow a second predetermined threshold level, the controller 18 actuatesonly the primary igniter assembly 100 a. The primary igniter assembly100 a, when actuated, ignites the primary propellant 110 a in theprimary combustion chamber 99 a. The primary propellant 110 a combustsand produces inflation fluid under pressure in the primary propellantchamber 99 a (FIG. 6). The pressure in the primary propellant chamber 99a rises rapidly.

The assembled secondary igniter cup 70 a and secondary cap 77 a duringthis time block flow of combustion products from the primary propellantchamber 99 a into the secondary propellant chamber 79 a. This preventsignition of the secondary propellant 210 a when the controller 18actuates only the primary igniter assembly 100 a.

The material thickness of the diffuser 30 a and closure 40 a is selectedso that the upper and lower walls 42 a end 62 a deform in response toinflation fluid pressure in the primary combustion chamber 99 a.Specifically, the upper wall 42 a of the diffuser 30 a deforms axiallyoutward (in an upward direction as viewed in FIG. 6). Simultaneously,the lower wall 62 a of the closure 40 a deforms axially outward in anopposite downward direction as viewed in FIG. 6. The degree to which thewalls 42 a and 62 a deform or deflect is dependent upon the pressure inthe primary combustion chamber 99 a. As the fluid pressure in theprimary combustion chamber 99 a increases, the degree to which the walls42 a and 62 a deflect also increases.

As the walls 42 a and 62 a of the diffuser 30 a and closure 40 a,respectively, move away from each other, the pressure of the inflationfluid in the primary propellant chamber 99 a forces the primary igniterassembly 100 a against the primary mounting portion 48 a of the closure40 a. The force exerted by the inflation fluid on the primary igniterassembly 100 a augments the weld connection and affects a fluid-tightseal between the primary igniter assembly 100 a and the closure 40 a.

As a result of the deformation of the walls 42 a and 62 a of thediffuser 30 a and closure 40 a, the distance between the upper wall 42 aof the diffuser and the lower wall 62 a of the closure increases.Therefore, the secondary igniter cup 70 a is no longer trapped axiallybetween the diffuser 30 a and the closure 40 a. The pressure of theinflation fluid in the primary propellant chamber 99 a, acting in adownward direction (as viewed in FIG. 6) on the secondary cap 77 a holdsthe secondary cap in engagement with the side wall 74 a of the secondaryigniter cup 70 a.

The inflation fluid flows out of the primary propellant chamber 99 a,through an annular filter 91 a, and toward the inflation fluid outlets56 a. The fluid outlets 56 a direct the inflation fluid to flow out ofthe diffuser 30 a to the air bag 14.

If the signal provided by the sensor 16 is above a second predeterminedthreshold level, greater than the first threshold level, the controller18 actuates both the primary igniter assembly 100 a and the secondaryigniter assembly 200 a. The actuation of the primary igniter assembly100 a results in ignition of the primary propellant 110 a, as describedabove. Inflation fluid produced by the primary propellant 110 a deformsthe diffuser 30 a and closure 40 a, and flows out of the inflator 10 a,as described above.

The secondary igniter assembly 200 a, when actuated, ignites thesecondary propellant 210 a. The secondary propellant 210 a producescombustion products that increase the pressure in the secondarycombustion chamber 79 a. This increased pressure acts on the secondarycap 77 a and causes the secondary cap to move out of engagement with theside wall 74 a of the secondary igniter cup 70 a (FIG. 7). This movementof the secondary cap 77 a is allowed due to the clearance created by thedeformation of the diffuser 30 a and the closure 40 a.

The combustion products of the secondary propellant 210 a are therebycombined with the combustion products of the primary propellant 110 a inthe primary combustion chamber 99 a. The resulting increase of pressurein the primary combustion chamber 99 a causes the diffuser 30 a andclosure 40 a to deform more than when only the primary propellant 110 ais ignited (FIG. 7). The combined combustion products of the secondarypropellant 210 a and the primary propellant 110 a flow through thefilter 91 a and out of the inflator 10 a in the manner described above.

The diffuser 30 a, the closure 40 a, the secondary igniter cup 70 a, andthe secondary cap 77 a are fabricated from sheet metal by a stampingprocess. The relative absence of machined or other precise tolerancefeatures within the inflator 10 a reduces production and assembly costswhile still maintaining the functional relationships between theinternal parts of the inflator 10 a.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications in the invention.Such improvements, changes end modifications within the skill of the artare intended to be covered by the appended claims.

Having described the invention, I claim:
 1. An apparatus for providinginflation fluid for inflating an inflatable vehicle occupant protectiondevice, the apparatus comprising: a primary housing constructed fromsheet metal by stamping; a primary inflation fluid source in the primaryhousing comprising a primary igniter assembly actuatable to effect aprimary flow of inflation fluid out of the primary housing to inflatethe inflatable device; a secondary housing constructed from sheet metalby stamping, the secondary housing being disposed within the primaryhousing such that the primary igniter assembly is positioned outside thesecondary housing; and a secondary inflation fluid source in thesecondary housing actuatable to effect a secondary flow of inflationfluid to supplement the primary flow of inflation fluid, the secondaryhousing having a first portion that moves at least partially out ofengagement with a second portion of the secondary housing when thesecondary inflation fluid source is actuated, wherein the first portionof the secondary housing comprises an upper end portion and the secondportion of the secondary housing comprises an opposite lower endportion, the upper end portion comprising a cap secured to the lower endportion and abutting an inner surface of the primary housing.
 2. Aninflator for providing inflation fluid for inflating an inflatablevehicle occupant protection device, the inflator comprising: a primaryhousing having an upper wall and a lower wall opposite the upper wall,the primary housing being constructed from sheet metal by stamping; aprimary inflation fluid source disposed within the primary housingactuatable to deform the primary housing to move the upper wall and thelower wall away from each other; a secondary housing constructed fromsheet metal by stamping and including an upper portion and a lowerportion, the secondary housing being disposed within the primaryhousing; and a secondary inflation fluid source comprising a secondaryigniter assembly centered within the secondary housing and actuatable tomove the upper portion of the secondary housing relative to the lowerportion of the secondary housing to release inflation fluid from thesecondary housing.
 3. The inflator as set forth in claim 2 wherein theupper portion of the secondary housing comprises a cap having aninterference fit with the lower portion of the secondary housing.
 4. Theinflator as set forth in claim 2 wherein the primary housing has aprimary circular opening for securing a primary igniter to the primaryhousing.
 5. The inflator as set forth in claim 4 wherein the primaryhousing has a secondary circular opening for securing a secondaryigniter to the primary housing.
 6. The inflator as set forth in claim 5wherein the secondary housing has a circular opening concentric with thesecondary circular opening of the primary housing.
 7. The inflator asset forth in claim 2 wherein the primary housing has a curved innersurface for securing the secondary housing within the primary housing.8. The inflator as set forth in claim 2 wherein the secondary housing issecured to the primary housing by an elastomeric seal.
 9. The inflatoras set forth in claim 2 wherein the primary housing comprises an upperportion and a lower portion welded to the upper portion.
 10. Theinflator as set forth in claim 2 wherein the primary housing includes arecessed mounting portion for securing a primary igniter to the primaryhousing.
 11. The inflator as set forth in claim 10 wherein the secondaryhousing includes a recessed mounting portion for securing a secondaryigniter to the secondary housing.
 12. The inflator as set forth in claim2 wherein the primary housing includes an annular mounting flange forsecuring the inflator to a vehicle.
 13. The inflator as set forth inclaim 2 wherein the upper portion of the secondary housing abuts theupper wall of the primary housing and the lower portion of the secondaryhousing abuts the lower wall of the primary housing prior to actuationof the primary inflation fluid source.
 14. The apparatus as set forth inclaim 2 wherein the upper wall of the primary housing is concave. 15.The apparatus as set forth in claim 2 wherein the primary inflationfluid source includes a primary igniter assembly positioned outside thesecondary housing.
 16. An apparatus for providing inflation fluid forinflating an inflatable vehicle occupant protection device, theapparatus comprising: a primary housing constructed from sheet metal bystamping; a primary inflation fluid source in the primary housingcomprising a primary propellant and a primary igniter assemblyactuatable to effect a primary flow of inflation fluid out of theprimary housing to inflate the inflatable device; a secondary housingconstructed from sheet metal by stamping, the secondary housing beingdisposed within the primary housing such that the primary igniterassembly is positioned outside the secondary housing, the primarypropellant being in contact with the primary igniter assembly and theprimary housing prior to actuation of the primary igniter assembly; anda secondary inflation fluid source in the secondary housing actuatableto effect a secondary flow of inflation fluid to supplement the primaryflow of inflation fluid, wherein the secondary inflation fluid sourceincludes a secondary igniter assembly centered within the secondaryhousing, the secondary housing having a first portion that moves atleast partially out of engagement with a second portion of the secondaryhousing when the secondary inflation fluid source is actuated.